This invention relates to ammonia converters for catalytically reacting a gaseous feed stream containing nitrogen and hydrogen to produce ammonia.
Elaborate and sophisticated reactor designs have been developed for converting nitrogen and hydrogen in the gas phase in a fixed catalyst bed to form ammonia. The designs have attempted to optimize the ratio of gas flow to catalyst volume for maximum catalyst effectiveness. Even so, it is still desirable to reduce the reactor size relative to the ammonia production capacity. The size of the reactor, of course, has an impact on its cost.
Ammonia converters are complicated by the fact that ammonia synthesis from nitrogen and hydrogen gas is exothermic and the reactions take place at high temperatures and pressures. Thus, interstage cooling is generally used between a series of catalyst zones to maintain kinetic and equilibrium conditions appropriate for optimum conversion efficiency. There must also be provision made for servicing the catalyst zones, e.g. periodically removing and replacing catalyst when it loses its effectiveness.
The use of the radial flow and mixed axial-radial flow arrangements in ammonia converter designs have become the standard for vertical ammonia converters. These designs, however, generally require the use of a freeboard or other catalyst volume that is ineffective. These designs can also complicate catalyst loading and removal, and require care in the design to avoid the potential for catalyst fluidization at the upper end of the radial flow catalyst volume.